"That their main business was not put into the mind knowledge which was not there before, but to turn the mind's eye towards light so that it might see for itself."
...Plato's advice to educators(429-347BC)

Things to try:1. wave speed, wave length and the speed of the point source can be adjusted2. Click near tip of the corresponding arrows and drag the mouse3. Click the mouse button within the window to suspend the animation, click it again to continue. The mouse position(related to initial poition) will be shown. Left click the mouse button and drag it to show the displacememt. Right click the mouse button and drag the mouse to show the angle.4. Click at the center of the red ruler to drag it. Click at either end and drag the mouse to change its length.5. Shock wave is formed if the point source moving faster than the wave speed.

Subject: Doppler effect and shock wave Date: Sat, 17 Jan 1998 20:49:55 +0700 From: Amrat Chawla <amratc@mozart.inet.co.th> To: hwang@phy.ntnu.edu.tw Dear Sir, Even though I am in trading business, in my personal time I am very much interested in Physics and I bought some 1st year university text book to study Physics as hobby. But frankly, your web site give me a very clear lesson just in few days that I discovered your site I understand a lot !!. For example I try to understand the sonic-boom but even I read many time I still cant get it, but with just few minute of virtual experiment with 'Doppler effect and shock wave' it became clear to me !! Really thankyou very much for your site. I regard you as my teacher. With respect and best rgds. Amrat Chawla

ubject: Your applets Date: Fri, 24 Jul 1998 13:13:16 -0400 From: diegel@med.unc.edu (Mike Diegel) To: hwang@phy03.phy.ntnu.edu.tw Fu-Kwun, My friend and I had been discussing what a sonic boom is and I was trying to describe how the sound waves come together to make it happen. We came across your web page at http://didaktik.physik.uni-wuerzburg.de/~pkrahmer/ntnujava/Doppler/Doppler.htmland used the applet. We thought it was a fantastic illustration of what a sonic boom is, and we just wanted to let you know that your work was appreciated. Thanks for the help. Mike Mike Diegel diegel@med.unc.edu 966-9100

The doppler applet is more flexibla now. I would though prefer if one could lefdt press and drag between 2 freely chosable points and get delta x, delta y; rather than only distance from source. Another detail is that the y coordinate is negative upwards which is not the most common matematically, though those distances aren't so interesting.

You might be interested to know that the doppler applet was referred to in one of the questions in the latest National Exam in Physics. But we aren't allowed to disclose the contents. (So erase this letter :-) )

I assume the index.html page was in Chinese (It sure wasn't English!)

The propagation applet is perfect. Whoops I just noticed that for large angles of incidence, the incident beam became solid red!

Subject: SV: SV: Doppler applet wish (&propagation) Date: Mon, 31 May 1999 05:43:14 +0100 From: Jeff Forssell <JF@ssvh.se> To: "'Fu-Kwun Hwang'" <hwang@phy03.phy.ntnu.edu.tw> I notice that if I enter a user ratio in propagation, the top and bottom field maintain the colors it had before, no matter whether the ratio is more or less that 1. Maybe it would be good to have the optically more dense media become gray.

I see that you have put in the angles also. I thought of suggesting that but I forgot to write it.

A new idea I got was is: could the intensity of the beam colors show how much of the radiation is reflected and transmitted. No big need, but it would be nice, even if just approximate. But that would be complicated because polarization comes in also. That would be a challenge! Maybe better with a separate applet. But you have made some amazingly compact versatile applets before. (Like the lens /mirror one!)

I think there maybe is a serious flaw in the doppler applet: example with the default settings the wavelength is supposed to be 20. If I measure on the right it is 20 and left it is 60 if i change the speed to 4 the measured distance between wavecrests becomes: 42 38 which seems to indicte that the wavelength is actually 40. I' m in a bit of a hurry until wednesday so I may have made a mistake.

if someone checks in the box, the user can place a "listner" anywhere in the window. Whenever a wavefront passes him the computer makes a sound (a beep or tick or something). For example: I place my listner in front of the advancing source: beep beep beep beep beep (then it passes) beep beep beep beep If I place my listener off to the side I would get a less pronounced effect (what should happen when a supersonic "bang" arrives should of course be some loud noise).

Another wish for the propagation applet: increase the n1/n2 options with "diamond to air". I think people tend to be fascinated by diamonds and they do have a spectacularly high n value. (I saw that in another persons refraction applet, which also included the possibility to show wavelength changes (also different colors for the different wavelengths) but I prefer yours otherwise)

Subject: Doppler applet wish (& propagation) Date: Wed, 26 May 1999 08:25:32 +0100 From: Jeff Forssell To: "'hwang@phy03.phy.ntnu.edu.tw'" I like the doppler applet (as I do most of your Javas) but when I was about to try to use the x,y coordinate display to measure the difference in apparent wavelength on different sides of the source, I found that the display changed to angle. Which is very good in some cases but it ought to be easy to have both. Either i 2 windows or perhaps left click= angle, right click=coordinates

Another wish would be that the "propagation applet (which I love!) could have the top medium become darker than the bottom when it´s n value is greater and increase the choice of n1/n2 to include day glass about air below. (I know and appreciate the possiblity to set the n/n ratio to 0.667, but if you feel like adding something I´d appreciate the above)

>---------- >Från: Fu-Kwun Hwang[SMTP:hwang@phy03.phy.ntnu.edu.tw] >Skickat: den 7 juni 1999 03:20 >Till: Jeff Forssell >Angående: Re: SV: SV: Doppler applet wish (& propagation) > ><><><><>propagation.class>> >Jeff Forssell wrote: > >> I notice that if I enter a user ratio in propagation, the top and bottom >> field maintain the colors it had before, no matter whether the ratio is >> more or less that 1. Maybe it would be good to have the optically more >> dense media become gray. >> >> I see that you have put in the angles also. I thought of suggesting >> that but I forgot to write it. >> >> A new idea I got was is: could the intensity of the beam colors show how >> much of the radiation is reflected and transmitted. No big need, but it >> would be nice, even if just approximate. But that would be complicated >> because polarization comes in also. That would be a challenge! Maybe >> better with a separate applet. But you have made some amazingly compact >> versatile applets before. (Like the lens /mirror one!) >> > >Try the attached java applet and let me know if this is what you want. >Pick p-wave or s-wave from the top left selection. > > >> >> I think there maybe is a serious flaw in the doppler applet: example >> with the default settings the wavelength is supposed to be 20. If I >> measure on the right it is 20 and left it is 60 if i change the speed >> to 4 the measured distance between wavecrests becomes: 42 38 which >> seems to indicte that the wavelength is actually 40. I' m in a bit of a >> hurry until wednesday so I may have made a mistake. > >In my previous java applet, the distance between wave front is not necessary >related to the wavelength. Those are wave front generate at fix time interval > not necessary equal to period of the wave). >In this attached java applet it is modified so that the wave front is >generated >with the same period of the wave. Try it and let me know what you think. > >I will try to add sound effect at the next release. >But you will have to wait a few days, >I will have to do other stuff first. > >

When I wrote a moment ago about a BASIC program I had and decimal acceptance, I got to thinking maybe your applet could be expanded (or a new one with similar components so It could replace this program for practicing reading analog scale instruments:

It is written i Qbasic. (There is also less common scale where range 12 V is to be interpretted from a printed scale with 6 V as full scale- I've seen similar things in reality but that aren't very common so I might take that away.) That I don't have more scale divisions depends on 2 things: 1) I want students to practice estimating tenths of scale divisions 2) lack of time (laziness?)

I m sending this qbasic file (and another on Vernier scale) As a friend of "old" computers I have versions for CGA and Hercules screens too

Yes we really do use commas for decimals! We even use (sometimes) periods as thousand separators. We do end our sentences with . though.

I was amazed to hear from you so quickly. I found myself wondering what is the time In Taiwan? We are at 17 degrees longitude and taiwan at 120 so that should mean that when you sent your letter it must have been around 6 pm your time. (I don't know if you use Daylight saving time there).

Both the class files were smaller than the old ones! How is that possible? Did you do some code cleaning when you added features?

My son has just used your very useful site for a middle school paper onsound waves. He really enjoyed experimenting with the frequencies andstudying the result. Never seen him enjoy science so much. Again, manythanks.

I thought it is not translated to English language. I am interested with it but I can't understand what's on it.

Because some one posted a question in Chinese, so I just posted previous message to tell him/her that we have more simulations in Chinese on our Chinese physics forum.When I created java applets for physics topics, I will create a Chinese version first. Then, I will add a English version when I have free time. So there are more applets in our Chinese forum , and there are many other multi-media for physics teaching,too. But I do not have time to translate all of then into English. Because I do all of this with my free time(after work). What I can promise is: If you need any simulation for physics teaching/learning and you can not find a similar one from the net, you can post it at Request for physics Simulations . I will try to create one for you as soon as possible.

i am a physics high school student.I've recently found your site.but I m unable to view the animation.A ctually I am not very handy with computer.Please show me the way to see the animations on all the topics.thankyou

Prof Hwang You mean i can use any simulation you design by jdk and translation to my local languageAnd publish in site without any probelm is java.class?Can you please explain how i do it because you design applets by jdk wonderful applets.

You can translate the strings in the simulations I have created with JDK1.0.2 by the following methods:1. If you know how to read the html source and find out the applet tag. Just change the value for parameter within applets tag should work.

2. For those who are not familar with html code.I already added an interface, you will find a new page shows up when you click download for offline use button.You will find interface for you to translate strings used by applets and html content.You can do the translation online. and the result will be sent to your email account.Just unzip the file and you will receive translated content.

You can upload the unziped files to your server and it should work fine.

"That their main business was not put into the mind knowledge which was not there before, but to turn the mind's eye towards light so that it might see for itself."
...Plato's advice to educators(429-347BC)